is a chemical element
that has the symbol Tm
and atomic number
69. A lanthanide
element, thulium is the least abundant of the rare earths
. It is an easily workable metal
with a bright silvery-gray luster and can be cut by a knife. It has some corrosion
resistance in dry air and good ductility
. Naturally occurring thulium is made entirely of the stable isotope
- Thulium has been used to create laser light but high production costs have prevented other commercial uses from being developed.
- High temperature superconductors use thulium as a better cathode than yttrium.
- Stable thulium (Tm-169) bombarded in a nuclear reactor serves as a radiation source in portable X-ray devices.
- The unstable isotope Tm-171 could possibly be used as an energy source.
- Tm-169 has potential use in ceramic magnetic materials called ferrites, which are used in microwave equipment.
Thulium was discovered
by Swedish chemist Per Teodor Cleve
by looking for impurities in the oxides
of other rare earth elements (this was the same method Carl Gustaf Mosander
earlier used to discover some other rare earth elements). Cleve started by removing all of the known contaminants of erbia
). Upon additional processing, he obtained two new substances; one brown and one green. The brown substance turned out to be the oxide of the element holmium
and was named holmia
by Cleve and the green substance was the oxide of an unknown element. Cleve named the oxide thulia
and its element thulium after Thule
Thulium was so rare that none of the early workers had enough of it to purify sufficiently to actually see the green color; they had to be content with observing the strengthening of the two characteristic absorption bands, as erbium was progressively removed. The first researcher to obtain nearly pure thulium was Charles James, a British expatriate working on a large scale at New Hampshire College in Durham NH. In 1911, he reported his results, having used his discovered method of bromate fractional crystallization to do the purification. He famously needed 15,000 "operations" to establish that the material was homogeneous.
High purity thulium oxide was first offered commercially in the late 1950's, as a result of the adoption of ion-exchange separation technology. Lindsay Chemical Division of American Potash & Chemical Corporation offered it in grades of 99% and 99.9% purity, priced at US $850 or $900, respectively, per pound as of January 1959. This was the same price being asked for comparable grades of europium or terbium oxide; only lutetium oxide cost more (among the rare earths). The minimum order was one gram (at $4.50 or $5.00, depending on purity).
The element is never found in nature in pure form, but it is found in small quantities in minerals
with other rare earths. It is principally extracted from monazite
(~0.007% thulium) ores found in river sands through ion-exchange
. Newer ion-exchange and solvent extraction techniques have led to easier separation of the rare earths, which has yielded much lower costs for thulium production. The principal source today are the ion adsorption clays of southern China. In the versions of these, where about two-thirds of the total rare earth content is yttrium, thulium is about 0.5% (or about tied with lutetium for rarity). The metal can be isolated through reduction
of its oxide
metal or by calcium
reduction in a closed container. None of thulium's natural compounds
are commercially important.
Naturally occurring thulium is composed of one stable isotope
, Tm-169 (100% natural abundance
). 31 radioisotopes
have been characterized, with the most stable being Tm-171 with a half-life
of 1.92 years, Tm-170 with a half-life of 128.6 days, Tm-168 with a half-life of 93.1 days, and Tm-167 with a half-life of 9.25 days. All of the remaining radioactive
isotopes have half-lifes that are less than 64 hours, and the majority of these have half lifes that are less than 2 minutes. This element also has 14 meta states
, with the most stable being Tm-164m (t½
5.1 minutes), Tm-160m (t½
74.5 seconds) and Tm-155m (t½
The isotopes of thulium range in atomic weight from 145.966 u (Tm-146) to 176.949 u (Tm-177). The primary decay mode before the most abundant stable isotope, Tm-169, is electron capture, and the primary mode after is beta emission. The primary decay products before Tm-169 are element 68 (erbium) isotopes, and the primary products after are element 70 (ytterbium) isotopes.
Thulium has a low-to-moderate degree of acute toxicity and should be handled with care. Metallic thulium in dust form presents a fire and explosion hazard.
Thulium is used as interstellar money in the book Illegal Aliens
(authors Nick Polotta
and Phil Foglio
), due to its rarity and lack of other uses.